Semiconductor devices such as an MOS (Metal Oxide Semiconductor) capacitor or a transistor are formed on a main surface of a semiconductor silicon wafer. A thickness of an insulator film such as a gate oxide film formed in such semiconductor devices is reduced with realization of high densities of the semiconductor devices and, on the other hand, decreasing a power supply voltage is difficult, whereby the insulator film is used with a high electric field intensity. Therefore, an insulator film having a higher quality is required.
As a reduction in film thickness of silicon oxide films involved by miniaturization advances, an unevenness allowable range for an oxide film thickness closes on a value corresponding to several atoms as an absolute value. Further, since insulation properties are degraded due to a direct tunnel current and gate leak increases in time of applying an electric field to an oxide film with a reduction in film thickness, new High-k materials have been studied with respect to a limit as the insulator film. However, in case that such new materials are used, a silicon oxide film is grown thinly and a High-k material is grown thereon. Therefore, accurately forming a thin oxide film is becoming more important.
An oxidation technique and others have been examined as control over growth of such an oxide film. Although a crystal orientation (B. E. Deal, J. Electrochem. Soc., 125, 576 (1978)., and E. A. Irene et. al., J. Electrochem. Soc., 133, 1253 (1986)., and S. I. Raider et. al., J. Electrochem. Soc., 127, 1783 (1980).) and a dopant (B. E. Deal et. al., 3. Electrochem. Soc., 112, 430 (1965)., and C. P. Ho et. al., J. Electrochem. Soc., 125, 665 (1978)., and Seong S. Choi et. al., Appl. Phys. Lett., 51, 1001 (1987)., and C. P. Ho et. al., J. Electrochem. Soc., 126, 1516, 1523 (1979).) and others are well known as influences of a silicon wafer itself, parameters other than those described above have been rarely reported in the era of a so-called ultrathin oxide film having a thickness of nearly 5 nm or below.
In regard to crystal orientation dependence, an oxidation rate has a relationship of <111>><100> irrespective of wet oxidation or dry oxidation. This plane orientation dependence of oxidation rate has been explained with a silicon atom density difference between crystal planes of respective plane orientations. A surface density is 7.85×1014(/cm2) in <111> while a surface density is 6.8×1014(/cm2) in <100>, and the oxidation rate rises as the surface density increases.
However, there is complexity between <110> plane and <111> plane. The surface density is 7.85×1014(/cm2) in <111> while a surface density is 9.6×1014(/cm2) in <110>, and an oxidation rate relationship can be assumed to be <110>><111> in terms of the surface density argument. This order is provided when an oxide film is as thin as approximately 15 nm, but the order is reversed and <111>><110> is achieved when the film thickness increases. Such a complicated behavior has been still argued.
Further, although a dopant acts in a direction along which the oxidation rate is accelerated, in more detail, if the dopant is phosphorus, a degree of an increase in oxidation rate rises as a temperature is reduced, and a rate increasing effect is decreased as the temperature is increased. Arsenic has the same tendency. On the other hand, in case of boron, the rate increasing effect is maintained even though the temperature is high.
Furthermore, according to recent studies (e.g, “Growth Kinetics of Very Thin Silicon Oxide Layers Monitored in Real-time by RHEED-AES” by Takakuwa, Surface Science, 23, 536 (2002).), models in which both vacancies that are point defects produced due to an interface damage and emitted Si atoms play the role of promoting an oxidizing reaction have been proposed. These models attempt an explanation of an oxidation mechanism in a thin-film region in particular which cannot be explained with a conventional Deal-Grove model as detailed analysis of the oxidizing reaction advances.
However, the above-described conventional parameters alone are insufficient to provide a uniform film thickness when forming, e.g., an ultrathin oxide film, and new parameters for accurately adjusting oxidizing conditions are required.